Italian scientists have found a ghostly image on the back of the shroud of Turin. Using sophisticated mathematical and optical techniques, they have exposed the faint imprint of the face and hands of the figure on the front of the cloth.

The discovery, reported in a British scientific journal today, is sure to resurrect the 600-year-old controversy over one of Christianity's most venerated but disputed relics.

The newly identified image, like the more dramatic one on the front of the cloth, is superficial, the scientists say. That is, the features are visible only on the outermost fibres of the fabric. "When a cross section of the fabric is made, one extremely superficial image appears above and one below, but there is nothing in the middle.

"It is extremely difficult to make a fake with these features," said Giulio Fanti, of the University of Padua.

The shroud is believed by many Catholics to be the cloth in which the body of Jesus was wrapped after crucifixion. It is a piece of linen - of a weave linked with first century Syria - on which the front and back images of an adult naked man are seemingly indelibly impressed. He seems to have been scourged, crowned with thorns, crucified with nails and stabbed in the side with a lance.

A branch of scholarship called sindonology, from the Italian word sindone which means shroud, has grown around it. Experts in recent decades have identified traces of blood, serum, myrrh, aloes and soil typical of Jerusalem on the shroud.

Others have claimed to have identified traces of madder, ochre and paint. The cloth has been damaged by folding, fire and water. It first appeared in France in the 14th century - the Pope at the time was in exile in Avignon - and a bishop of Troyes in 1386 claimed to know for certain that it had been "cunningly painted".

In 1988 the Vatican permitted three laboratories in Oxford, Zurich and Tucson each to take a tiny sample of the cloth for radiocarbon dating. All three labs separately found that the flax from which the linen was woven had grown between AD1260 and 1390.

But many shroud scholars were unwilling to accept that the shroud was therefore a fake. One group argued that some miraculous event could have "reset" the carbon clock in the shroud's fabric. Another has claimed that the radiocarbon dating could have been wrong in all three cases. A third has claimed that the samples sent to the laboratories had mistakenly been taken from cloth used to restore the shroud in the medieval period.

Professor Fanti and Roberto Maggiolo of Padua University's department of mechanical engineering report in the Journal of Optics A: Pure and Applied Optics, published by the Institute of Physics in London, that they worked from a photograph taken by a churchman in 2002 while the backing cloth was being replaced during restoration.

The paper originally submitted to the journal is believed to have contained more speculation about how the images might have been formed. Some scientists have argued that the imprint could have been made by a "corona discharge" between a corpse and a wrapping sheet when the corpse was immersed in an electric field.

One sindonologist has more directly proposed that the image on the cloth was the result of an intense source of energy as the body passed through the cloth, perhaps at the moment of resurrection.

In the published paper, the two scientists argue only that the so-called double superficiality - the imprint on both sides of the cloth but not within the fabric itself - will "be taken into account in a future explanation".